The present invention relates to a device and a method for stabilizing a vehicle.
SAE Paper No. 973284 entitled xe2x80x9cVehicle Dynamics Control for Commercial Vehiclesxe2x80x9d describes a device for stabilizing a commercial vehicle designed as a tractor-trailer composed of a tractor vehicle and a semi-trailer. The float angle and the yaw rate of the tractor vehicle and buckle angle between the tractor vehicle and the semi-trailer are controlled. For this purpose, a system deviation between the actual values and the setpoint values for the float angle, the yaw rate and the buckle angle are determined. Engine interventions and/or brake interventions are initiated as a function of these system deviations to stabilize the tractor-trailer.
The article entitled xe2x80x9cFDRxe2x80x94Die Fahrdynamikregelund von Boschxe2x80x9d (Vehicle Dynamics Control by Bosch), published in the journal xe2x80x9cAutomobiltechnische ZeitschriftSxe2x80x9d,(ATZ) [Journal of Automotive Technology] 96, Vol. II, pp. 674-689, 1994 describes such a stabilization device for passenger cars. In this stabilization device only the yaw rate and the float angle of the vehicle are taken into consideration for control.
Neither the conventional device for stabilizing the tractor-trailer nor the conventional device for stabilizing a passenger car provides for adjustment of the variation over time of the setpoint values for the quantities to be controlled to the behavior of the vehicle. This results in the following disadvantage: for example, if the driver of the vehicle performs a steering motion, experience shows that a certain period of time elapses before the vehicle follows this steering motion and performs the desired cornering, for example, i.e., attains the steady-state condition initialized by the steering motion. If the setpoint values are determined using appropriate vehicle models describing the steady-state condition as a function of the steering angle without time adjustment, the setpoint values of the steady-state condition are present from the very beginning. However, since the instantaneous actual state of the vehicle does not correspond to the steady-state condition, at least immediately after the steering motion has been initiated, a system deviation occurs, resulting in inappropriate and unnecessary control interventions, which would not be performed if the variation of the setpoint values over time were adjusted to the vehicle behavior.
An object of the present invention is to improve existing devices and methods for stabilizing vehicles and forming the system deviation.
The device according to the present invention includes first determining means with which at least two vehicle motion quantities describing the motion of the vehicle, in particular in the direction transverse to that of travel, are determined. These vehicle motion quantities correspond to the actual values mentioned previously. In addition, the device includes second determination means with which a characteristic quantity corresponding to the above-mentioned setpoint value is determined for each of the vehicle motion quantities. The characteristic quantities describe the vehicle behavior intended by the driver. Furthermore, there are control means with which intervention quantities are determined at least as a function of the vehicle motion quantities and the characteristic quantities. These intervention quantities are sent to actuator means for performing at least brake interventions and/or engine interventions with which the vehicle is to stabilized.
In order to achieve the improvement in forming the system deviation, the second determination means have adjusting means with which the variation of the characteristic quantities over time is adjusted to the vehicle behavior. This means that in forming the characteristic quantities, it is taken into account that the vehicle does not immediately assume a steady-state condition, but only assumes it after a certain period of time.
Since the characteristic quantities also describe the steady-state condition of the vehicle after a certain period of time, the second determination means advantageously include calculation means with which final values for the characteristic values are determined. These final values correspond to the values of the vehicle motion quantities present in the steady-state condition of the vehicle. The final values are sent to the adjustment means and the characteristic quantities are determined as a function of these final values.
It has been found that the final values are advantageously determined at least as a function of a steering angle quantity describing the steering angle set for the vehicle and a velocity quantity describing the velocity of the vehicle. The velocity of the tractor vehicle is advantageously considered the vehicle velocity.
The above discussion shows that the variations over time of the characteristic quantities are adjusted to the vehicle""s behavior so that the characteristic quantities advantageously attain their respective final values only after a predefined period of time that is characteristic for the vehicle.
Regarding the period of time characteristic for the vehicle, two procedures are advantageous: either the period of time is fixed or it is determined at least as a function of one of the quantities describing the vehicle""s behavior.
Advantageously, there also are two procedures for adjusting the variation over time of the characteristic quantities. In the first procedure the variations over time of all characteristic quantities are adjusted to the vehicle""s behavior in the same manner using the adjusting means. In this case the time periods after which the characteristic quantities attain their final values are the same for all characteristic quantities. This procedure can be used when the vehicle exhibits the same behavior over time, concerning assuming the steady-state condition, for all vehicle motion quantities for which control is performed. In the second procedure the variation over time of each individual characteristic quantity is separately adjusted to the vehicle""s behavior. This procedure is required when the vehicle exhibits different conditions over time for the vehicle motion quantities for which control is performed.
The adjustment means are designed, for example as filtering means with which the variation of the characteristic quantities over time is influenced by defining a filter constant.
It is advantages if an all pass filter is used as filtering means. The phase and thus the variation of the characteristic quantities over time can be modified using an all-pass filter without modifying the value, i.e., the amplitude of the characteristic quantity. The same holds true if a low-pass filter that has a very low limit frequency is used as a filtering means.
As mentioned previously, the final values are determined at least as a function of a steering angle quantity and a velocity quantity. Vehicle models/mathematical models are used for this purpose. Some of the parameters used in these models are determined at least as a function of vehicle quantities and/or vehicle parameters.
The vehicle quantities advantageously include at least one mass quantity and/or at least one center of gravity position quantity. This ensures that, in determining the characteristic quantities, the influence of different load conditions is taken into account. This means that the different vehicle conditions are advantageously recognized and taken into account in the control. For tractor-trailers one mass quantity and one center of gravity position quantity are advantageously determined for both the tractor vehicle and the trailer or semi-trailer. Geometry parameters and/or tire side rigidity quantities are used as vehicle parameters, since most of these parameters have a non-negligible effect on the vehicle""s behavior.
The control means contained in the device have different individual controllers. In the control principle implemented, one of these individual controllers influences the others and/or one of these controllers controls the others. This principle has the advantage that proven individual controllers can be used for the controlled or lower-order individual controllers.
It also is advantageous if the value of at least part of the final values is limited. These values are limited as a function of a transverse acceleration quantity describing the transverse acceleration acting on the vehicle, and/or a function of the longitudinal acceleration quantity describing the longitudinal acceleration acting on the vehicle, a function of a friction coefficient quantity describing the instantaneous friction coefficient between the road surface and the tires, or a function of wheel force quantities describing the forces acting on the wheels of the vehicle.
The device according to the present invention can be used for both single vehicles and tractor-trailers. If the vehicle in which the device according to the present invention is used is a tractor-trailer that has a tractor vehicle and the trailer or semi-trailer, three vehicle motion quantities are determined using the first determining means. Two of these vehicle motion quantities describe the condition of the trailer vehicle and one of these vehicle motion quantities describes the position the behavior of the trailer or semi-trailer with respect to the tractor vehicle. Specifically in this case a yaw rate quantity describing the yaw rate of the of the tractor vehicle is used as a first vehicle motion quantity, a float angle quantity describing the float angle of the vehicle is used as a second vehicle motion quantity, and/or a buckle angle quantity describing the buckle angle between the tractor vehicle and the trailer or semi-trailer is used as a third vehicle motion quantity.
If the vehicle in which the device according to the present invention is used is a single vehicle, a yaw rate quantity and/or a float angle quantity are determined as vehicle motion quantities.
It should be pointed out here how the float angle of the vehicle is geometrically defined as the angle between the direction of the vehicle velocity at the center of gravity of the vehicle and the longitudinal axis of the vehicle.
It also may be advantageous if the device according to the present invention includes a trailer and/or semi-trailer detector that automatically detects whether a trailer or semi-trailer is attached to the tractor vehicle.
In addition to the above-mentioned brake interventions and engine interventions, chassis interventions or transmission interventions can also be used to stabilize the vehicle.